1. Field of the Invention
The present invention relates to a method of fabricating a nitride-based semiconductor light-emitting device and a nitride-based semiconductor light-emitting device, and more particularly, it relates to a method of fabricating a nitride-based semiconductor light-emitting device having a nitride-based semiconductor layer formed on a nitride-based semiconductor substrate and a nitride-based semiconductor light-emitting device.
2. Description of the Background Art
A nitride-based semiconductor light-emitting device such as a nitride-based semiconductor laser diode having a nitride-based semiconductor layer formed on a GaN substrate employed as a nitride-based semiconductor substrate is known in general, as disclosed in Japanese Patent Laying-Open No. 2000-58972, for example.
The aforementioned Japanese Patent Laying-Open No. 2000-58972 discloses a nitride-based semiconductor laser diode formed by successively growing an n-type nitride-based semiconductor layer, a light-emitting layer and a p-type nitride-based semiconductor layer on an n-type GaN substrate having a planar surface. In the conventional nitride-based semiconductor laser diode disclosed in the aforementioned Japanese Patent Laying-Open No. 2000-58972, an n-type cladding layer formed on the n-type GaN substrate as the n-type nitride-based semiconductor layer has a structure obtained by alternately stacking 100 n-type AlGaN layers and 100 undoped GaN layers with each other.
In the conventional nitride-based semiconductor laser diode disclosed in the aforementioned Japanese Patent Laying-Open No. 2000-58972, however, the quantity of cracks formed on the n-type AlGaN layers is disadvantageously increased when the n-type AlGaN layers constituting the n-type cladding layer are grown on the n-type GaN substrate having the planar surface. More specifically, when an n-type AlGaN layer 202 grown on an n-type GaN substrate 201 having a planar surface as shown in FIG. 32 is strained due to the difference between the lattice constants of the n-type GaN substrate 201 and the n-type AlGaN layer 202, it is difficult to relax this strain. When the n-type AlGaN layer 202 is grown on the n-type GaN substrate 201 having the planar surface, therefore, the quantity of cracks 203 formed on the n-type AlGaN layer 202 to extend in the [11-20] direction (see FIG. 34) and the [1-210] and [−2110] directions (see FIG. 34) equivalent to the [11-20] direction is increased as shown in FIG. 33. Referring to FIG. 34, θ is 120°.
When the quantity of cracks formed on the n-type AlGaN layers (n-type nitride-based semiconductor layer) is increased in the nitride-based semiconductor laser diode disclosed in the aforementioned Japanese Patent Laying-Open No. 2000-58972, a large number of cracks are disadvantageously formed also on the light-emitting layer and the p-type nitride-based semiconductor layer successively formed on the n-type nitride-based semiconductor layer. In the nitride-based semiconductor laser diode disclosed in the aforementioned Japanese Patent Laying-Open No. 2000-58972, therefore, a large number of cracks formed on a nitride-based semiconductor device layer including the n-type nitride-based semiconductor layer, the light-emitting layer and the p-type nitride-based semiconductor layer disadvantageously increase a leakage current not supplied to a light-emitting portion of the nitride-based semiconductor device layer and hinder a transmission of a light. Consequently, the characteristics and the yield of the nitride-based semiconductor laser diode are disadvantageously reduced in the nitride-based semiconductor laser diode disclosed in the aforementioned Japanese Patent Laying-Open No. 2000-58972.